Showing papers on "Incubation published in 1984"

The Effects of Reducing Conditions, Medium, pH, Temperature, and Time on in Vitro Excystation of Cryptosporidium

Abstract: . Whereas excystation of sporozoites from oocysts of most coccidian species requires exposure to reducing conditions followed by pancreatic enzymes and bile salts, sporozoites of a bovine isolate of Cryptosporidium excysted without exposure to either reducing conditions or to pancreatic enzymes and bile salts. Without prior exposure to reducing conditions, a high percent excysted after incubation in a mixture of trypsin and bile salts in Ringer's solution; fewer excysted after incubation in tap water, even fewer after incubation in salt solutions, and none after incubation in saliva. Excystation, generally greater at pH 7.6 than at pH 6.0 and at 37°C than at 20°C, was observed as early as 1 h after incubation in water or the trypsin-bile mixture. These findings provide circumstantial evidence that oocysts of Cryptosporidium can excyst in extraintestinal sites and liberate sporozoites that can initiate autoinfection.

Storage of the Eggs of the Fowl (Gallus domesticus) before Incubation: A Review

Abstract: The literature relating to storage of hatching eggs prior to incubation is reviewed under 5 headings:— 1. Storage time—prolonged storage leads to reduced hatchability and also produces a longer inc...

Metabolic stability of hippocampal slice preparations during prolonged incubation

Abstract: Hippocampal slices were prepared under three conditions: (1) in medium containing glucose and oxygen at 4 degrees C; (2) as in (1), but at 37 degrees C; (3) in medium devoid of glucose and oxygen at 37 degrees C. The rates of recovery to roughly steady-state levels and through 8 h of incubation were monitored for energy metabolite levels and related parameters. In vitro stable values are compared with in situ hippocampal levels. Regardless of the conditions under which slices were prepared, metabolite levels required up to 3 h to stabilize, and these levels were maintained or improved through 8 h of incubation. Further, the maximal concentrations of metabolites were independent of the conditions of slice preparation. Total adenylates and total creatine levels reached 55% of those in vivo. Lactate decreased from the decapitation-induced high levels, but stabilized at concentrations about twice those in rapidly frozen brain. Cyclic AMP and cyclic GMP exhibited peak levels at 30 min of incubation, and cyclic GMP remained elevated for 3 h. Although all three methods of slice preparation resulted in similar metabolite profiles on incubation, the initial decreases in high energy phosphates were delayed by chilling. Most striking, the slices prepared in the absence of glucose and oxygen exhibited much smaller orthodromic evoked potentials in the dentate gyrus. The presence of glucose and oxygen during preparation of the slices appears to be critical to the electrophysiological response of the tissue.

Regulation of prolactin and its role in gallinaceous bird reproduction

Abstract: There are major changes in circulating luteinizing hormone (LH), prolactin (PRL), estrogens (E), and progesterone (P) in relation to the onset of reproduction, egg laying, incubation, and care of young. LH levels increase in the prelaying period, followed some days later by increased circulating levels of E, P, and PRL. Levels of these hormones tend to stabilize during egg laying with periodic ovulatory cycle changes. Around the onset of incubation PRL levels increase, while LH, E, and P levels fall. During incubation PRL reaches very high levels, falling sharply when incubation is terminated. Stimulatory effects of hypothalamic neurotransmitters, peptides, and ovarian steroids on PRL secretion have been shown. The prelaying increase is dependent on E and P and the high levels of incubation require a functional serotonergic system. The causal relationships and roles of PRL in incubation of gallinaceous birds are, however, still unclear.

Energetics of Embryonic Development in the Megapode Birds, Mallee Fowl Leipoa Ocellata and Brush Turkey Alectura lathami

Abstract: Mallee fowl (MF) and brush turkey (BT) lay large, energy-rich eggs (173 g at 10.2 kJ/g contents for MF and 180 g at 9.8 kJ/g contents for BT) that are incubated by burial in mounds of warm earth or decaying vegetation. Their incubation periods of 62 days (MF) and 49 days (BT) are unusually long, and their hatchlings are among the most precocial of any birds. Metabolic rates of embryos of both species just prior to hatching are about 61 cm³ O₂/h, 98% (MF) and 64% (BT) higher than predicted. Metabolism is supported solely by chorioallantoic respiration until hatching, and pulmonary respiration begins suddenly when the shell membranes are torn. Estimates of total energy expenditure during incubation prior to hatching ($E_{i}$) based on O₂ consumption closely approximate estimates based on energy content of fresh eggs and hatchlings. The $E_{i}$ are high (∼600 kJ for MF and ∼475 kJ for BT) because of the long incubation periods. Hatchlings must dig out of the incubation mounds, and costs of this may add 8% (M...

In vitro 11-ketotestosterone and 17α,20β-dihydroxy-4-pregnen-3-one production by testicular fragments and isolated sperm of rainbow trout, Salmo gairdneri

Abstract: Two different testicular tissue preparations, testicular fragments and isolated sperm were incubated in the presence or absence of chumsalmon gonadotropin (SGA, lμg/ml), 17μ-hydroxyprogesterone (17μ-OHprog, 0.1 μg/ml) and testosterone (T, 0.1 μg/ml). 11-Ketotestosterone (11-keto T) and 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) in the incubation medium were measured by specific radioimmunoassay. Incubation of testicular fragments with SGA, 17α-OHprog or T resulted in a highly significant increase in 11-keto T levels in the incubation medium. Sperm preparations did not produce 11-keto T under any incubation condition. Both testicular fragments and sperm preparations produced large amounts of 17α,20β-diOHprog when incubated with 17α-OHprog. SGA slightly stimulated 17α,20β-diOHprog by testicular fragments but not by sperm preparations. These results suggest that different testicular elements are the sites of synthesis of 11-keto T and 17α20β-diOHprog. Furthermore, it is suggested the involvement of sperm in the production of 17α,2Oβ-diOHprog in the testis of spermiating rainbow trout.

Shedding of gangliosides from tumor cells depends on cell density.

Abstract: The ganglioside composition of mouse ascites hepatoma (MAH) cells, the ascites fluid and cell-conditioned media were determined and found to be qualitatively identical, but quantitatively different The ganglioside content of the ascites fluid and the medium conditioned by MAH-cells at the native cell concentration (108 cells/ml) comprised respectively 749% and 23% of the cell-associated gangliosides When incubated at lower cell-density (106 cells/ml) the cells were found to be release about three-times higher amounts of ganglioside per cell than during incubation at the native concentration Centrifugation of the dense-cell-conditioned medium revealed the major part of the released gangliosides to be associated with a 150000 x g pellet that probably contains shed plasma membrane fragments In the 150000 x g pellet of the extracellular fluids the relative content of the most polar cell ganglioside corresponding chromatographically to GT1b was about ten-times higher than in the cells The possibility is raised that the more intense shedding of gangliosides from less crowded MAH cells may play a role in the self protection of the tumor from host immune rejection during initial stages of growth

Relationship between activation and phosphorylation of tyrosine hydroxylase by 56 mm K+ in PC12 cells in culture.

Abstract: Incubation of rat pheochromocytoma PC12 cells with 56 mM K+ is associated with increased activity and enhanced phosphorylation of tyrosine hydroxylase in the cells. The increase in the phosphorylation of tyrosine hydroxylase is observed after 30 sec of incubation with 56 mM K+; maximal phosphorylation is observed after 1 min of incubation. In contrast, although a significant increase in the activity of tyrosine hydroxylase is demonstrable after 30 sec of incubation with 56 mM K+, maximal activation is not attained until 3 min of incubation. Both the activation and increased phosphorylation of tyrosine hydroxylase exhibit a similar dependence upon potassium concentration in the incubation medium and are dependent on the presence of extracellular calcium. These results suggest that, although there is a relationship between activation and phosphorylation of tyrosine hydroxylase after potassium-evoked depolarization of rat pheochromocytoma PC12 cells in culture, this relationship may be complex.

Acidification and liming of coniferous forest soil: Long-term effects on turnover rates of carbon and nitrogen during an incubation experiment

Abstract: Forest soils from field plots, subjected to long-term acidification by H 2 SO 4 treatment, or to liming, were examined for the effects of treatment on net mineralization and turnover rates of carbon and nitrogen during incubation. The total soil respiration was decreased as a result of acidification, whereas the proportion of labeled C, introduced as 14 C-glucose at start of the incubation, was increased in the CO 2 pool emitted. The accumulation of mineral N (ammonium) was not significantly influenced by acidification, whereas the rate of microbial N turnover, obtained from 15 N-dilution data for the exchangeable NH 4 + fraction, was markedly decreased.

Inverse changes in plasma prolactin and LH concentrations in female canaries after disruption and reinitiation of incubation.

Abstract: Prolactin and LH concentrations were measured in the plasma of female canaries sampled during the breeding cycle and after disruption and reinitiation of incubation behaviour. The late incubation period was characterized by low LH and high prolactin concentrations, and canaries separated from their nests at this stage showed an increased in LH and a decline in prolactin within 3 h. In one experiment mean (+/- S.E.M.) concentrations before and 24 h after nest deprivation were: prolactin 397 +/- 86 and 18 +/- 5 micrograms/l; LH 1.04 +/- 0.21 and 2.03 +/- 0.17 micrograms/l. Female canaries which abandoned their nests after the eggs had been removed also showed an increase in LH together with a fall in prolactin 24 h after egg removal. When nest-deprived canaries were allowed to resume incubation, plasma prolactin increased again within 5 h and after 2 days had reached levels normal for incubating birds (398 +/- 46 micrograms/l). Concentrations of LH changes more gradually but had decreased 2 days after the resumption of incubation. Thus prolactin and LH show inverse changes after the disruption and reinitiation of incubation behaviour; it is not clear, however, if the change in one is dependent on the other or if both hormones are responding to the same external stimulus.

Prolactin and parenting in the pigeon family

Abstract: The relationship between plasma prolactin and: (1) crop growth; (2) incubation; (3) brooding; and (4) feeding young in Columbiformes is reviewed. There is a good parallel between changes in crop growth and plasma prolactin fluctuations during the breeding cycle. Prolactin does not play a role in the initiation of incubation, though it can maintain the response. Toward the end of breeding, a decline in prolactin precedes the decline in incubation (of infertile eggs) or brooding (of young), while exogenously administered prolactin can prolong the response. There is no evidence of a necessary relationship between prolactin secretion and parental feeding of young, as this behavior can precede and outlast the secretion of the hormone during breeding.

Incubation in the Starling, Sturnus Vulgaris: Resolution of the Conflict Between Egg Care and Foraging

Abstract: Complementary studies on Starlings nesting on the Frisian island Schiermonnikoog included estimation of total energy expenditure of the parent birds, evaluation of the cost of incubation, experiments on the effect of manipulated nest temperature on incubation rhythm, and observation of prey intake rates during foraging trips. Typically the eggs were covered 95% of the time, and experimentally it could be shown that a fall in nestbox temperature elicited an increase in sitting activity. It is argued that this relation is brought about by responsiveness to egg temperature at the outset of the sitting spell, as this will determine the shape of the warming curve and hence the time until equilibrium incubation temperature has been restored. In years of poor food supply the parents compensated by making longer foraging trips and extending their active day. An inter-season comparison suggests that the length of the foraging trip is set to collect a given amount of food. In years of high densities of the principal prey (larvae of Tipula paludosa) and hence high intake rates, the parents spent more time in alternate feeding sites thereby constituting a more varied diet. In the year of poorest food supply the sitting bout was extended to allow the off-duty partner sufficient time to collect food. In rich years some females managed to incubate unassisted. The energy cost of incubation involves a modest increment in the daily energy budget. Flight at this time is greatly reduced and this savings more than offsets the cost of heating the eggs, such that during incubation the parent birds probably enjoy the lowest demand of any phase of the breeding cycle. The main problem posed by incubation is thus how to collect enough food in the time available, rather than coping with excessive energetic costs.

Regulation of the Synthesis of Barley Aleurone α-Amylase by Gibberellic Acid and Calcium Ions

Abstract: The effects of gibberellic acid (GA(3)) and calcium ions on the production of alpha-amylase and acid phosphatase by isolated aleurone layers of barley (Hordeum vulgare L. cv Himalaya) were studied. Aleurone layers not previously exposed to GA(3) or Ca(2+) show qualitative and quantitative changes in hydrolase production following incubation in either GA(3) or Ca(2+) or both. Incubation in H(2)O or Ca(2+) results in the production of low levels of alpha-amylase or acid phosphatase. The addition of GA(3) to the incubation medium causes a 10- to 20-fold increase in the amounts of these enzymes released from the tissue, and addition of Ca(2+) at 10 millimolar causes a further 8- to 9-fold increase in alpha-amylase release and a 75% increase in phosphatase release. Production of alpha-amylase isoenzymes is also modified by the levels of GA(3) and Ca(2+) in the incubation medium. alpha-Amylase 2 is produced under all conditions of incubation, while alpha-amylase 1 appears only when layers are incubated in GA(3) or GA(3) plus Ca(2+). The synthesis of alpha-amylases 3 and 4 requires the presence of both GA(3) and Ca(2+) in the incubation medium. Laurell rocket immuno-electrophoresis shows that two distinct groups of alpha-amylase antigens are present in incubation media of aleurone layers incubated with both GA(3) and Ca(2+), while only one group of antigens is found in media of layers incubated in GA(3) alone. Strontium ions can be substituted for Ca(2+) in increasing hydrolase production, although higher concentrations of Sr(2+) are required for maximal response. We conclude that GA(3) is required for the production of alpha-amylase 1 and that both GA(3) and either Ca(2+) or Sr(2+) are required for the production of isoenzymes 3 and 4 of barley aleurone alpha-amylase.

Estradiol regulation of secretory component in the uterus of the rat: evidence for involvement of RNA synthesis.

Abstract: The present studies were undertaken to characterize the response of uterine secretory component (SC) to estradiol. Administration of estradiol for 3 days to ovariectomized rats before incubation of uterine tissues resulted in a marked accumulation of SC in the incubation media. When uteri from ovariectomized rats treated with progesterone or testosterone were incubated, very little SC accumulated in the media, indicating that the estradiol-stimulated increase is hormone-specific. When uteri from rats that received estradiol for 6 days were compared with uteri from 3-day treated rats, SC release during a 24-hr incubation period was the same. This finding indicates that in the presence of prolonged estradiol exposure, SC production continues. The estradiol-induced accumulation of SC in culture is not due to the release of pre-formed uterine SC. When tissue SC levels were measured after 3 days of estradiol treatment, very little tissue SC was found relative to that released into culture media during 24 hr of incubation. The addition of actinomycin D to the incubation media markedly inhibited SC release by uteri from estradiol-treated rats. The release of SC was also inhibited by alpha-amanitin, a known inhibitor of Type II polymerase. These studies demonstrate that estradiol stimulation of SC is markedly reduced by inhibitors of RNA synthesis, and suggest that estradiol regulation of SC is mediated through uterine mRNA synthesis.

Egg temperature and embryo metabolism in some high-latitude procellariiform birds

Abstract: The embryos of Procellariiformes develop slowly, reportedly, at least in part, as a result of low incubation temperatures, and some species such as Wilson's and Leach's storm petrels experience long periods of chilling. Incubation temperatures of eggs of Leach's storm petrel (on Kent Island, New Brunswick), Wilson's storm petrel, and the southern giant fulmar (Palmer Station, Antarctica) averaged 35.9, 35.7, and 35.5 C, respectively. These are well within the range of temperatures for other species of birds and indicate that the prolonged incubation periods of petrels are not attributable to low incubation temperatures. We measured the depressing effect of cooling ($Q_{10}$) on rate of heartbeat of small embryos and rate of oxygen consumption of larger embryos. Values of $Q_{10}$ increased at lower temperatures but in most cases did not differ from, or in some cases even exceeded, the values for embryos of species that lack cooling tolerance. Large embryos of the giant fulmar, which has slow embryonic dev...

Coupling of physiology of embryonic turtles to the hydric environment

Abstract: Embryonic turtles developing in flexible-shelled eggs consume more of their yolk and grow larger before hatching when incubated in relatively wet environments than they do when incubated in relatively dry settings. These differences in size of young result from differences in rates of embryonic metabolism and growth in some species and from differences in duration of incubation in others. However, neither the specific physical factor eliciting the responses nor the underlying physiological mechanism has been established unequivocally for any species. Because embryos in relatively wet environments have different patterns of net water-exchange than do embryos in drier settings, most attention has been directed at means by which such exchanges could influence their physiology. Water exchanges may exercise control over oxidative metabolism by altering bulk water in cytoplasm of cells of growing animals, by affecting concentrations of urea in body fluids of embryos, by influencing growth of the allantois, and, indirectly, by affecting incubation temperature; water fluxes may influence duration of incubation via effects on water potential in compartments such as the yolk. However, the evidence to support these hypotheses is fragmentary, and no single mechanism is applicable to all species studied to date.

Interferon receptor interaction

Abstract: Studies reported earlier [ Joshi et al. (1982) J. Biol. Chem. 257, 13884-13887] have indicated that human interferon-alpha 2 (HuIFN-alpha 2) binds to a specific macromolecular receptor on human cells as identified by cross-linking with bifunctional cross-linking reagents and analysis by polyacrylamide gel electrophoresis. We have carried out experiments to investigate the fate of the interferon-receptor complex on the cell surface under conditions which lead to cellular response. As analyzed by cross-linking and gel electrophoresis, the interferon-receptor complex, formed on incubation with 125I-IFN-alpha 2 at 4 degrees C, persisted at the cell surface for several hours at 4 degrees C; however, if the cells were switched to 37 degrees C, there was a rapid decline in the complex, apparently due to a loss of the interferon receptors from the cell surface. This was associated with an internalization of the 125I-interferon as indicated by the fact that, on incubation at 37 degrees C, an appreciable fraction of the cell-associated interferon (approximately equal to 50%) became resistant to trypsin digestion, or dissociation on incubation in growth medium or low-pH buffer. A large fraction of the trypsin-resistant (internalized) 125I-labeled material migrated as intact interferon in polyacrylamide gels, and it was immunoprecipitated by anti-(HuIFN-alpha)antibodies but not by anti-(HuIFN-beta)antibodies. The bulk of the internalized 125I-interferon was recovered in a particulate fraction and, on cross-linking with disuccinimidyl suberate, a 150000-Mr complex could be detected. The results suggest that interferon may be internalized as a complex with the receptor, which may account for the loss of the interferon-receptors on the cell surface. This modulation of the IFN-alpha/beta receptors was induced by HuIFN-alpha and HuIFN-beta but not by HuIFN-gamma. The recovery of the IFN-alpha/beta receptors, lost upon incubation with HuIFN-alpha, took several hours and required protein synthesis. The significance of the results is discussed.

Effect of photoinhibition during bottle incubations on the measurement of seasonal primary production in a shallow coastal water

Abstract: Primary productivity in Vineyard Sound. Massachusetts (USA), a shallow well-mixed coastal water, was determined at monthly intervals during May-October. 1981. Over the course of each study day fresh samples first were obtained at 3 h intervals and then incubated until sunset with timecourse measurements of Hl4C0; uptake made at frequent intervals. Two seasonal patterns of 14C uptake were apparent. First, rapid initial uptake of I4C over each incubation during the spring and fall was followed by reduced uptake during periods of strong sunlight. The duration over which rapid uptake was sustained was a function of the prevailing light intensity at the start of the incubation. Under these conditions estimates of near surface primary productivity based on summing total production over the first 3 h of each back to back incubation were higher by 50 to 130 % than estimates based on single end-point measurements from full-day incubations. During summer, however, uptake of I4C was linear throughout each incubation when both total daily irrad~ation and temperature were maximal so that the 2 techniques for estimating productivity led to comparable results. The reasons for these seasonal differences in the pattern of I4C uptake are unclear, but may be related to changes in temperature or phytoplankton species, or both. Our results for a shallow well-mixed water are in general accord with the conclusion of Harns (1980) that when vertical mixing is sufficient to prevent prolonged exposure of phytoplankton to photoinhibiting light intensities at the surface, photoinhibition could be far more pronounced during a bottle incubation than is occurring in the water column.

Microbial biomass in soil: Effects of some experimental variables on biochemical estimations

Abstract: The effects of experimental variables on estimates of biomass C and mineral-N (Min-N) flush by the chloroform fumigation technique were determined in near neutral to slightly alkaline topsoil samples of a Typic Haplaquoll taken at three different times under grazed grass-clover pastures. The variables were soil mesh size ( < 3.3 and < 2 mm), water content [50 and 60% of water-holding capacity (WHC)], the use of samples that were “fresh” or that had been previously incubated (7 days at 50% of WHC at 25°C), and, for the biomass C estimates, various incubation periods for measuring CO2C production. Estimates of biomass C were most strongly influenced by the incubation period selected for CO2C production by unfumigated soil. The effects of soil mesh size and water content were significant for some samples, but were not consistent. Prior incubation lowered all biomass C estimates significantly, except for some samples where a 0–10 day period was used for measuring CO2C production by unfumigated soil; (the presence or absence of soda-lime during incubation had no influence on subsequent rates of CO2 production by the unfumigated samples). Min-N flush was not consistently influenced by these variables, although some significant treatment effects occurred. Biomass C-to-Min-N flush ratios were predictably dependent upon the biomass C estimates used. They averaged 9.0 in “fresh” samples and 6.0 in incubated samples, when the incubation periods for CO2C production by unfumigated samples were 10–20 and 0–10 days respectively. Results indicate that care should be taken in interpreting and comparing biochemical indices of microbial biomass, and their ratios, obtained by different or modified experimental procedures.

5β-Reductase activity in the brain and cloacal gland of male and female embryos in the Japanese quail (Coturnix coturnix japonica)

Abstract: Testosterone metabolism was studied by an in-vitro technique in the brain and cloacal gland of young male and female quail at different ages ranging from 7 days of incubation to 2 days after hatching. Very active metabolism, leading almost exclusively to the production of 5 beta-reduced compounds, was observed. 5 beta-Reductase activity remained high throughout the incubation period in the hypothalamus, decreased around the time of hatching in the cerebellum and decreased progressively between days 7 and 15 of incubation in the cloacal gland. These changes could be involved in the control of sexual differentiation: the high 5 beta-reductase in the brain possibly protects males from being behaviourally demasculinized by their endogenous testosterone while the decreasing 5 beta-reductase in the cloacal gland would progressively permit the masculinization of that structure.

Reduced Fc-receptor function in human monocytes exposed to ethanol in vitro.

Abstract: Mononuclear phagocytes from healthy human donors were incubated with or without ethanol (12–55 mM, initial concentration) in non-sealed wells in an atmosphere of 5% CO2 in air for 6 or 24 hr on day 1 or day 7 in culture. The actual ethanol concentration was assayed in the media at the beginning and at the end of each incubation period. The ethanol content was reduced to about 70% of the initial concentration after 6 hr incubation, and to below 20% after 24 hr incubation. Binding properties of the Fc-receptors, and their associated phagocytic activity, were tested after ethanol exposure of the cells. An initial concentration of 12 or 22 mM ethanol caused no differences from controls at any time in culture. Mononuclear phagocytes assayed on day 1 (=monocytes) showed reduced binding (60% of control) as well as internationalization (70% of control) of particles via the Fc-receptors after addition of 55 mM ethanol and incubation for 6 or 24 hr. Incubation in corresponding ethanol concentration for 6 hr had no effect on cells cultured for 7 days (=macrophages), whereas 24 hr incubation depressed the Fc-receptor function in these cells also. There were no changes in viability, morphology or spreading ability after ethanol treatment.

The age distribution of legg-perthes disease an analysis using sartwell's incubation period model

Abstract: The etiology of Legg-Perthes disease of the hip is unknown. One current hypothesis suggests that an environmental factor affects the growth mechanism at a critical prenatal stage. The time interval between the critical exposure and the onset of clinical disease can be regarded as the incubation period, and the distribution of ages at onset of disease will reflect the distribution of incubation periods. Published series of cases were examined for fit to Sartwell's logarithmic normal model of incubation periods. All fit except two. The study results are consistent with a single cause acting at a critical stage of life, i.e., before two years of age. The findings are compatible with either a prenatal or postnatal influence.

Effect of thermotolerance on thermal radiosensitization in hepatoma cells.

Abstract: The interaction between hyperthermia and X irradiation was determined in cultured Reuber H35 hepatoma cells with different states of thermosensitivity Incubation at 41/sup 0/C followed by 4-Gy X rays resulted after 2 hr in a stabilization of cell survival for heat or heat plus X rays, with a maximum synergism factor of 16 Thermotolerance did not develop during incubation at 417 or 425/sup 0/C When heat treatment of cells was followed by irradiation, the synergism factor for thermal radiosensitization increased with both the amount of thermal cell killing and the amount of X-ray cell killing; the influence of thermal exposure on the synergism factor was greater than that of the X-ray dose Cells were made thermotolerant either by incubation at 425/sup 0/C for 30 or 60 min followed by an interval at 37/sup 0/C, or by continuous incubation at 41/sup 0/C In both cases thermotolerance was measured by incubation at 425/sup 0/C No difference was observed between the maximum thermotolerance achieved with both methods When cells were irradiated in addition to the second heat treatment, thermal radiosensitization was strongly reduced concomitant with the decreased sensitivity to killing by heat

Availability of carbon-bonded sulfur for mineralization in forest soils

Abstract: The capacities of soil from hardwood, clear-cut, and pine forests of the Coweeta basin to mineralize, adsorb; and incorporate into Organic matter carbon-bonded sulfur in the form of L-methionine was investigated. These soils adsorbed and incorporated between 40 and 66% of this amino acid within a 0.5-h incubation period, but much of the immobilized sulfur was mineralized after 48 h incubation. Ah additional hardwood forest (watershed 18) was chosen for further study of the incorporation process in both litter and mineral horizons. The O2 forest floor layer exhibited the highest levels of activity in samples taken along a transect of this watershed. Incorporation of methionine into the organic matter of these samples was complete within about 12 h of incubation and was inhibited by pretreatment of the samples with sodium azide; a general inhibitor of cell respiration. The capacities for methionine incorporation determined invitro complement observations of the high levels of carbon bonded sulfur found insi...

Influence of Hydration of the Environment on the Pattern of Nitrogen Excretion by Embryonic Snapping Turtles (Chelydra Serpentina)

Abstract: SUMMARY Flexible-shelled eggs of common snapping turtles were incubated on wet and dry substrates. More than 70 % of the waste nitrogen accumulating in eggs on both substrates was in the form of urea, and less than 25 % was in the form of ammonia. Low levels of soluble urate were detected in eggs late in incubation, but insoluble urate was never present. Accumulation of ammonia and soluble urate was unaffected by the hydration of the environment, but more urea accumulated late in incubation in eggs on the wet substrate than in those on the dry substrate. Thus, embryos are ureotelic throughout development, and the pattern of accumulation of the primary nitrogenous waste is influenced by hydration of the environment.